/*
 *  Copyright (c) WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
 *
 *  WSO2 Inc. licenses this file to you under the Apache License,
 *  Version 2.0 (the "License"); you may not use this file except
 *  in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.wso2.balana.xacml3;

import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.wso2.balana.*;
import org.wso2.balana.ctx.AbstractResult;
import org.wso2.balana.ctx.AttributeAssignment;
import org.wso2.balana.ctx.EvaluationCtx;

import java.io.OutputStream;
import java.io.PrintStream;
import java.net.URI;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;

/**
 * Represents the AdviceExpressionType XML type in XACML. Advice are introduced
 * with XACML 3
 */
public class AdviceExpression {

	/**
	 * The value of the advice identifier may be interpreted by the PEP.
	 */
	private URI adviceId;

	/**
	 * The effect for which this advice must be provided to the PEP.
	 */
	private int appliesTo;

	/**
	 * Advice arguments in the form of expressions;
	 * <code>AttributeAssignmentExpression</code>
	 */
	private List<AttributeAssignmentExpression> attributeAssignmentExpressions;

	/**
	 * Constructor that takes all the data associated with an AdviceExpression .
	 * 
	 * @param adviceId
	 *            the advice's id
	 * @param appliesTo
	 *            the effect for which this advice must be provided
	 * @param attributeAssignmentExpressions
	 *            a <code>List</code> of
	 *            <code>AttributeAssignmentExpression</code>s
	 */
	public AdviceExpression(URI adviceId, int appliesTo,
			List<AttributeAssignmentExpression> attributeAssignmentExpressions) {
		this.adviceId = adviceId;
		this.appliesTo = appliesTo;
		this.attributeAssignmentExpressions = attributeAssignmentExpressions;
	}

	/**
	 * Creates an instance of <code>AdviceExpression</code> based on the DOM
	 * root node.
	 * 
	 * @param root
	 *            the DOM root of the AdviceExpressionType XML type
	 * @param metaData
	 *            policy meta data
	 * @return an instance of an <code>AdviceExpression</code>
	 * @throws ParsingException
	 *             if the structure isn't valid
	 */
	public static AdviceExpression getInstance(Node root,
			PolicyMetaData metaData) throws ParsingException {

		URI adviceId;
		int appliesTo;
		String effect;
		List<AttributeAssignmentExpression> expressions = new ArrayList<AttributeAssignmentExpression>();
		NamedNodeMap attrs = root.getAttributes();

		try {
			adviceId = new URI(attrs.getNamedItem("AdviceId").getNodeValue());
		} catch (Exception e) {
			throw new ParsingException(
					"Error parsing required attribute AdviceId "
							+ "in AdviceExpressionType", e);
		}

		try {
			effect = attrs.getNamedItem("AppliesTo").getNodeValue();
		} catch (Exception e) {
			throw new ParsingException(
					"Error parsing required attribute AppliesTo "
							+ "in AdviceExpressionType", e);
		}

		if (effect.equals("Permit")) {
			appliesTo = AbstractResult.DECISION_PERMIT;
		} else if (effect.equals("Deny")) {
			appliesTo = AbstractResult.DECISION_DENY;
		} else {
			throw new ParsingException("Invalid Effect type: " + effect);
		}

		NodeList nodes = root.getChildNodes();
		for (int i = 0; i < nodes.getLength(); i++) {
			Node node = nodes.item(i);
			if (node.getNodeName().equals("AttributeAssignmentExpression")) {
				try {
					AttributeAssignmentExpression expression = AttributeAssignmentExpression
							.getInstance(node, metaData);
					expressions.add(expression);
				} catch (Exception e) {
					throw new ParsingException(
							"Error parsing attribute assignments "
									+ "in AdviceExpressionType", e);
				}
			}
		}

		return new AdviceExpression(adviceId, appliesTo, expressions);
	}

	/**
	 * returns whether this is applied for permit or deny
	 * 
	 * @return permit/deny
	 */
	public int getAppliesTo() {
		return appliesTo;
	}

	/**
	 * returns advice id
	 * 
	 * @return advice id
	 */
	public URI getAdviceId() {
		return adviceId;
	}

	/**
	 * return evaluation result of the advice expression
	 * 
	 * @param ctx
	 *            <code>EvaluationCtx</code>
	 * @return result as <code>Advice</code> Object
	 */
	public Advice evaluate(EvaluationCtx ctx) {
		List<AttributeAssignment> assignments = new ArrayList<AttributeAssignment>();
		for (AttributeAssignmentExpression expression : attributeAssignmentExpressions) {
			Set<AttributeAssignment> assignmentSet = expression.evaluate(ctx);
			if (assignmentSet != null && assignmentSet.size() > 0) {
				assignments.addAll(assignmentSet);
			}
		}
		return new Advice(adviceId, assignments);
	}

	/**
	 * Encodes this <code>AdviceExpression</code> into its XML form and writes
	 * this out to the provided <code>OutputStream<code> with no indentation.
	 * 
	 * @param output
	 *            a stream into which the XML-encoded data is written
	 */
	public void encode(OutputStream output) {
		encode(output, new Indenter(0));
	}

	/**
	 * Encodes this <code>AdviceExpression</code> into its XML form and writes
	 * this out to the provided <code>OutputStream<code> with indentation.
	 * 
	 * @param output
	 *            a stream into which the XML-encoded data is written
	 * @param indenter
	 *            an object that creates indentation strings
	 */
	public void encode(OutputStream output, Indenter indenter) {
		PrintStream out = new PrintStream(output);
		String indent = indenter.makeString();

		out.println(indent + "<AdviceExpression AdviceId=\""
				+ adviceId.toString() + "\" AppliesTo=\""
				+ org.wso2.balana.ctx.xacml2.Result.DECISIONS[appliesTo]
				+ "\">");

		indenter.in();

		if (attributeAssignmentExpressions != null
				&& attributeAssignmentExpressions.size() > 0) {
			for (AttributeAssignmentExpression assignment : attributeAssignmentExpressions) {
				assignment.encode(output, indenter);
			}
		}

		indenter.out();

		out.println(indent + "</AdviceExpression>");
	}
}
